1. Field of the Invention
This invention relates to a refrigerant evaporator with a drain structure, particularly suitable for an automotive air conditioner.
2. Description of the Related Art
As shown in FIG. 11, a refrigerant evaporator has plural tubes 2 and corrugated fins 5 respectively disposed between two adjacent tubes 2 and joined thereto. Each of the tubes 2 is composed of two aluminum thin plates 4, which are joined to each other to form a passage therebetween. Each of the corrugated fins 5 is formed from a corrugated aluminum thin plate, and has louvers, which are cut and bent-up from the plate with a specific angle. The louvers improves a thermal conductive efficiency of the fin 5. Meandering inner fins 42, 43 are disposed in and joined to the tubes 2 to improve a thermal conductive efficiency at a refrigerant side.
In the refrigerant evaporator, a central drain groove 10 and a downstream side drain groove 11 are provided at the central portion and a downstream end portion of the tube 2 in an air flow direction A to improve a condensed water draining performance. JP-Y2-4-22225 proposes a similar structure of the evaporator. However, this drain structure is insufficient to drain condensed water from the evaporator. Especially, referring to FIG. 12, condensed water produced at the air upstream side fin and flowing on inner surface angular portions 5c of bent portions 5b of the fin 5 is difficult to be drained and may clog root portions of the louvers 5a.
FIGS. 14A and 14B show an experimental result revealing the problem described above. Experimental conditions were 2.0 m/s in flow rate V of air flowing into a core part 3 of the evaporator, 30.degree. C. in temperature of the air, 60% in relative humidity RH of the air, and 4 mm in fin pitch fp of the corrugated fin 5. FIG. 14A shows air flow paths at a dry state where no condensed water is produced on the surface of the corrugated fin 5, and at a wet state where condensed water is produced on the corrugated fin 5 to clog the louvers 5a. At the dry state, since the louvers 5a are not clogged with condensed water, air can pass through the louvers 5a to the downstream side end. As opposed to this, at the wet state, air cannot pass through the louvers 5a provided between a middle portion to the downstream side end of the fin, because condensed water clogs the louvers 5a. As a result, as shown in FIG. 14B, an air side heat conductivity at the wet state is decreased by approximately 15% as compared to that at the dry state.
On the other hand, recently, a size reduction is required to an automotive air conditioner so that a space for installing the air conditioner in a vehicle compartment is reduced. Therefore, the refrigerant evaporator is also required to be size-reduced especially in the air flow direction A. To comply with this requirement, the refrigerant evaporator must be improved to have higher capacity. Generally, increasing an air side thermal conductivity largely improves the evaporator capacity, and the air side thermal conductivity is increased by decreasing the fin pitch. Decreased fin pitch increases a thermal conductive area. When the fin pitch is decreased, however, water holding capacity of the fin is increased to facilitate the clogging of the louvers by condensed water, resulting in deterioration of fin thermal conductivity.